There's been a spate of "improve your sex life" books recently, most of which fall into the "wink wink, nudge nudge" category. Sexual Intelligence takes a much more sensible approach. It's about understanding your own sexual history and views of sex and how they contribute to your ability to have fulfilling, meaningful intimate relationships. That said, I've got some problems with this book.
The core of the book is a study where the authors correlated people's sexual history and attitudes to their current situation. By naming this correlation "sexual intelligence" they imply that's it's some kind of "sex IQ", when a number of factors that have nothing to do with "intelligence", including your personal history, are taken into account.
Also, as a caveat, the book doesn't have anything to say about what's right or wrong in sexual conduct. This is about factors that correlate with satisfaction. I applaud the fact that intimacy, love, and care are all given their due, however this book isn't a guide in how to conduct your life vis-a-vis sex.
For example, in the section on affairs at work, the book notes that "sexually intelligent" people report they've had intimate relationships with co-workers that turned out great, while for people who did not score high on the sexual intelligence scale, such affairs turned out badly—a rather ambiguous conclusion at best.
Nevertheless, this book is full of useful information and a number of good case studies, without a puerile slant.